Cathode and method of preparing the same



l934-l I D. v. EDWARDS EFAL 1,985,355

CATHODE AND METHOD OF PREPARING THE SAME Filed 'July 30, 1932 IN V EN TORS DMDM Maw/Q Km/KM Lari- 16 W 11- @061;

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Mata D... 25, 1934 1,985,855

UNITED STATES PATENT OFFICE 1,985,855 oa'rnom-z AND METHOD errant-name 'mn sum Donald V. Edwards, Montclair, and Earl K. Smith, East Orange, N. 1., minors to Electrons, Inc. of Delaware, a corporation of Delaware Application July 30, 1932, Serial No. 626,618

15 Claims. (Cl. 25027.5)

This invention relates to electron emissive temperature of about 300 to 400 C. to remove cathodes and method of preparing same, and has the water before subjecting the core to higher special utility for cathodes in gaseous discharge temperatures. The coating then has a white tubes having control electrodes. color.

In the operation of discharge tubes of the type The white coated core is then further heated in 5 known as control tubes in which the starting of air or in the presence of oxygen to a temperature an arc discharge between the cathode and anode of approximately 800 C., to convert the major is controlled by a third .element, it is important portion of the coating to barium oxide. A simple that the various operating characteristics of the method for heating the core consists in passing tube shall remain constant throughout its life. a suitable current through it. After the coating 10 In some applications there are periods of nohas been oxidized, the temperature of the core load with the cathode heated; in such case it is then increased to approximately 900 C. which often happens that the point of control will shift changes the coating to a compound having a more and more from that which is normal for the black color and a granular structure, as illus l5 tube, until control is completelylost. trated at 12. A further increase in temperature One of the causes of such difliculty is the vato approximately 1000 0. causes the black, granporization of highly electro-positive metals and ular coating to melt and dissolve in the core, as the deposit thereof upon the normally nonemisindicated at 13. During the several heating steps sive electrodes. Such vaporization occurs, in it is preferable to have a draft of air passing over coatings containing barium, at temperatures as the core. 0 low as 600 C. Upon cooling, the core has a lustrous black The object of the present invention is to devise surfacehaving the appearance of a vitreous film a cathode and method of making the same, such thereon. The barium compound thus formed is that the cathode will have a high degree of stanot confined to the core surface however, but

bility with minimum vaporization of the electropenetrates the surface and includes a portion of 2 positive metal, at temperatures above the melting the core metal in its composition. point of the electro-positive metal. At this stage of the treatment the cathode In carrying out our invention we form a core may be assembled in a tube. The treatment is of suitable base metal, such as nickel, and dissolve then continued by heating the cathode to aptherein an emissive compound of ahighly electroproximately 1100 C. in the presence of some 30 positive metal which is soluble in the core metal. uncombined barium oxide, which is usually left The chemical changes which take place have not on the ends of the cores, while maintaining a been exactly determined but they are evidenced vacuum with a suitable pump. The heating in to the unaided eye by changes in appearance and vacuum completes the conversion of the coating color of the treated core. compound and causes a further change in the 35 One embodiment of the invention has been seblack compound 13 to the ultimate form, in lected for the following description which should which the cathode surface takes on the appearbe read in connection with the accompanying ance of' a metallic lustre similar to metallic drawing, inwhich nickel, as indicated at 14.

40 Fig. 1 represents a portion of a cathode or fila- The excess of oxygen in the cathode compound 40 ment, embodying the invention, in several stages is removed by the pump, together with any other of its treatment; and v gases which are liberated from the electrodes by Fig. 2 illustrates a similar filament formed into the usual process of degassing.

a coil. Each step of the aforementioned heating in A core, preferably of nickel, is formed to the air may be performed in a few seconds or con- 5 shape and size which it will have in the cathode tinued for several minutes, the core being allowed structure of which it is to be part, and is heated to cool between step 1 t mperature of the in air to oxidize its surface. Such a' core is illuscoated core may b Continuously increased u l trated at 10 in Fig. 1. A coating 11, which prefthe condition illustrated at 13 is obtained. The

erably consists of an alkaline earth carbonate or heating in vacuum and degassing is continued 50 a mixture .of suchcarbonates in the form of a until the cathode is in proper emissive-condition. water paste is applied to the core. A preferred In the condition shown at 14, the cathode comsubstance is carbonate of barium, and a suitable prises a nickel core having a. soluble compound, amount is approximately 6% by weight of the which we believe to be barium nickelate, discore material. The coating is dried in air at a solved therein. To the best of our knowledge 7 55 the soluble compound has the chemical composition BaO.NiO and is not the commonly known di-nickelate BaO.2(NiOz), sometimes referred to as barium nickelite.

We have reason to believe that any compound of one of the alkaline-earth metals with oxygen and one of the metals of the iron group, which is soluble in the latter metal and which is not volatile at the temperature at which the emission of the alkaline-earth metal would be sufficient, may be substituted for the compound of nickel, barium and oxygen above mentioned.

A form of filament for retaining some uncombined barium oxide after the coated filament has passed through the aforementioned steps of heating in air, is shown in Fig. 2 in which a core 15 is formed into a coiled filament. When heating current is passed through the coil an excess of barium oxide is automatically left on the end turns due to the center portion of the wire being hotter than the end portions. Therefore, the black compound is formed and melted more quickly on the center portion of the coil, the end portions still being in the uncombined condition. When such a coiled filament is heated in vacuum the excess barium oxide on the endscombines with the excess oxygen in the middle and the compound disappears into the core as the dissolved nickel-barium-oxygen compound.

It should be understood that the core may be composed in whole or part of nickel or another metal of the iron group, in which the alkaline earth metal is soluble, so long as its surface is composed of such a metal to a depth suiiicient to constitute a reservoir of emissive compound to meet the required life of the cathode. The central or inner portion of the core may contain a more refractory metal.

Instead of leaving some uncombined oxide on the filament after it has passed through the aforementioned steps of heating in air, it is sometimes desirable to continue the heating until all of the coating compound is converted to the black compound 13, in which case the desired compound is formed and the excess oxygen re moved by heating the core in a reducing atmosphere, such as hydrogen. After the hydrogen treatment the cathode is assembled in the tube and degassed in the usual manner.

Filling the tube with inert gas and bombarding the cathode while it is heated to about 1000 C. or 1100 C. speeds up the final stage of the oathode treatment.

Instead of forming the black compound 13 on the core as above described, an alternative process is to make, separately, a similar compound comprising barium, nickel and oxygen, which is soluble in the core metal and then to dip the core into the molten compound under conditions permitting the solution of the emissive compound in the core metal.

Cathodes as above described have a high degree of stability, and are free from the effects of electrolysis and from consequent wide variation in initial velocity of electrons leaving the cathode surface. With such cathodes the arc drop quickly reaches equilibrium when load is suddenly applied, and'loss of grid control in control tubes, after idleness with filament lighted and no load, is avoided.

A modification of the ideas and general principles disclosed herein, employing similar compounds and a similar hydrogen treatment, is dis closed and claimed in our application, Serial Number 754,590, filed November 24, .1934, said Loeaess application being a continuation in part of the present application.

We claim:

1. The method of preparing an electron emissive cathode which comprises forming a soluble nonvolatile compound of a highly electro-positive metal and dissolving substantially all of the said compound in a core having, for its surface, a metal of the iron group.

2. The method of preparing an electron emissive cathode which comprises coating a nickel core with barium carbonate, causing the carbonate to be changed to a compound soluble in the core, and dissolving the said compound in the core.

3. The method of preparing a cathode for an electron discharge tube which comprises coating a nickel core with a compound of barium, heating the core in the presence of oxygen to convert said compound into barium oxide, continuing the heating at higher temperatures until in the pres ence of oxygen the coating melts and is dissolved in the core, and then heating in vacuum to a still higher temperature.

4. The method of preparing a cathode for an electron discharge tube which comprises coating a nickel core with barium carbonate, heating in air to approximately 800 centigrade whereby the white carbonate changes to the oxide, and heating in air at temperatures from 900 to1000 centigrade until substantially all of the coating becomes black in color and is absorbed by the nickel core, and further heating in Vacuum to approximately 1100" centigrade.

5. The method of making an emissive cathode which comprises forming on the surface of a core a compound containing an alkaline earth metal. a metal of the iron group and oxygen, the said core consisting of a metal of the iron group, and dissolving said compound in the core.

6. The method of making an emissive cathode which comprises forming on the surface of a nickel core a compound consisting of barium, nickel and oxygen, dissolving said compound in the core, and heating the same in vacuum.

7. The method of making an emissive cathode which comprises applying a compound of barium on the surface of a nickel core, heating the core in the presence of oxygen and forming thereon a black compound of nickel, barium and oxygen, heating to a higher temperature until the black compound dissolves in the core, and subsequent- 1y heating the core in vacuum at approximately 1100 centigrade until substantially all gas is removed therefrom and the core has a metallic lustre similar to nickel.

8. The method of making an emissive cathode which comprises applying a compound of barium on the surface of a nickel core, heating the core in the presence of oxygen and forming thereon a black compound of nickel, barium and oxygen, heating to a higher temperature until the black compound dissolves in the core, and subsequently heating in a reducing atmosphere.

9. An electron emissive cathode comprising a nickel core having dissolved therein barium nickelate.

10. An electron emissive cathode comprising a nickel core containing in solution therein a compound of nickel, barium and oxygen in which the barium is securely bound at temperatures up to 900 centigrade, whereby the barium is not evaporated from said core below said temperature.

11. An emissive cathode comprising a comall all

pound of one o! the alkaline earth metals with a metal of the iron group and oxygen, the melting point of said compound being above 875 centigrade, and a core of metal of the iron group containing the said compound in solution therein.

12. An electron emissive cathode comprising a core of ametal of the iron group containing in solution therein a barium compound which is non-volatile up to 900 centigrade, said compound consisting of barium, a metal of the iron group and oxygen. 13. An electron emissive cathode comprising a metallic core and a compound of one of the metals of the iron group with an alkaline earth metal and oxygen, the said core containing the said compound in solution therein.

mamas 14. The method of making an emissive cathode which comprises applying a compound containing an' alkaline earth metal, a metal 0; the iron group and oxygen, on a core surface consisting of a metal of the iron group, and dissolving said compound in the core.

l5.- The steps in the preparation of an electron emissive cathode which comprise coating a metal core with a compound of highly electro-positive metal and heating the same in the presence of oxy en until the coating melts and runs into the solid core metal. 

